Inverted v-beam antenna system



March 22 Filed Dec.

YII

F. WINTER 3,242,491

INVERTED V--BEAM ANTENNA SYSTEM 3 Sheets-Sheet 1 A Z s" Zenith CHARLES E W//VTER ATTORNEY March 22, 1966 Filed Dec. 12, 1962 C. F. WINTER INVERTED V-BEAM ANTENNA SYSTEM SsSheets-Sheet 2 /lVl/ENTO? CHARLES E W/NTE'? ATTORNEY 1 I I I I I l March 22, 1966 c. F. WINTER INVERTED Vi-BEAM ANTENNA SYSTEM 3 Sheets-Sheet 5 Filed Deo. l2, 1962 COMPUTER DISPLAY LA N N DE MN .5w EET IE TPM TT RA R H EN WSM VA N u {NVIB R 3 R 9 E X .\5 .vm S5 X u W DI P D w w C R R M 9 FIh R m n R H E W )N V .w M w M .u .uw 6 m m C A E A E R R R R T T A 5 NVENTO? CHARLES E' WINTER y #M M AT'ORNEY United States Patent O 3,242,491 INVERTED V-BEAM ANTENNA SYSTEM Charles F. Winter, Wrentham, Mass., assigner to Raytheon Company, Lexington, Mass., a corporation of Delaware Filed Dec.k 12, 1962, Ser. No. 244,059 14 Claims. (Cl. 343-11) The present -invention relates to shaped beam antenna systems, and, more particularly, to a system which orients at least one beam of a plurality of shaped beams along a small circle arc.

The majority of three-coordinate guidance and detection antenna systems lack the capability of handling an unlimited number of airborne vehicles, particularly for landing operations requiring accurate angles of descent unless preselected azimuth and elevation approach bearings are utilized. For t-he prior shaped beam antenna art, see, Antenna Engineering Handbook, Henry lasik, McGraw-Hill Book Company, Inc., 1961, particularly chapter 9, etc., and Microwave Antenna Theory and Design, Samuel Silver, Editor, McGraw-Hill Book Company, Inc., 1949, particularly chapter 13 and chapter 12, Simple Fanned-Beam Antennas, inasmuch as a fanned beam is considered a shaped beam for the purposes of this invention, for a detinition and explanation of shaped beams and the types of antennas which can be used to radiate shaped beams. This art teaches a V-beam antenna system which shows the greatest potential for meeting the problem of handling an unlimited number of airborne vehicles. The V-beam approach towards meeting this problem of provid-ing target elevation dates back to World War II; however, to the present time, the disadvantages have outweighed the advantages.

The simple V-beam radiation coverage consists of two distinct beams, each of said beams lying on great circles of a sphere and having their antennas positioned at the center of said sphere no matter what position either of the antennas radiating the beams are slanted, and both shaped in their vertical directions and of narrow beam widths in any azimuthal plane. The definition of a great circle and a small circle are found in Websters New International Dictionary, 2nd edition unabridged, which under the heading of Circles of Sphere statesA a circle upon the surface of the sphere, specifically of. the earth or of the heavens, called a great circle when its plane passes through the center of. the sphere; in all other cases, a small circle, is adopted in this specification as being definitive of the above words, great circle and small circle. One beam is koriented in the conventional shaped-beam Search fashion, i.e., the plane in which the shaping occurs makes an angle of 90 with the horizon plane for any azimuthal pointing of the antenna. The other beam is tilted over at a slant, i.e., its plane of shaping makes an angle of less than 90 with the horizon. When this beam system rotates at a constant rate about the vertical axis, a stationary airborne vehicle may be hit by radiations from both antennas. The angle between hits (which can be determined by a time measurement) can be seen to be a function of the elevation angle of the airborne target. If the tilt angle of the slant antenna is known, then it is possible to solve for the tangent of the angle between beam lhits and, therefore,

3,242,491 Patented Mar. 2,2., 1966 ICC establish a relationship between elevation angle versus the angle between beam hits so as to, at all points, determine the angle of descent of said airborne vehicle.

The principal disadvantages of a simple V-beam antenna are that the highest elevation angle that can be determined is a function of the tilt angle. A large tilt angle with respect to the horizontal severely limits elevation coverage for two reasons. First, the slant beam never rises above the complement of the tilt angle. Second, the angle between hits becomes progressively wider as the elevation angle increases. Furthermore, the rate of change of the slope for each radiation curve is a minimum at low elevation angles and, therefore, sensitivity is least near the horizon instead of at the higher angles where accuracy for ground based applications is typically less critical. Additionally, the difference between slope angles on any radiation curve at two elevation angles represents the amount of rotation that aV linearly polarized eld vector undergoes and, therefore, for a one way beacon V-beam transmission approach, signal loss at the receiving antenna generally results because of the misalignment between the polarizations of the receiving and transmitting antennas.

Therefore, an object of the invention is to provide an improved antenna system which is capable of providing accurate elevation measurements over a broad range of angles and simultaneously of providing the greatest sensitivity of measurement at the low elevation of angles.

In accordance with this invention, an inverted V-shaped beam antenna system, such as used in a beacon guidance system, comprises a transmitter providing energy to a first means for radiating a shaped beam along a great circle and to a second means for radiating a shaped beam along a small circle. Additionally, a system used as a three dimensional or 3D radar, having height finding as one of its functions, comprises a first transmitter, providing energy to an isolation means, such as a dupleXer to a first means for radiating a shaped beam along a great circle and a second transmitter, providing energy through a second isolation means to a second means for radiating a shaped beam along a small circle, and a receiver-computer coupled to each of said isolation means for determining a targets position in 3D. By radiating at least one of the beams along a small circle which passes through or suiciently close to the zenith, the spread between the two beams decreases with increasing elevation, and sensitivity is greatest near the horizon.

For a better understan-ding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, wherein:

FIG. 1 illustrates a geometry for an inverted V-beam antenna system showing arcs of radiation along two small circles,

FG. 2 illustrates a beacon helicopter system in block form utilizing an inverted V-shaped beam antenna,

FIG. 3 illustrates a geometry of the Ibeacon helicopter system of FIG. 2 having an inverted V-shaped lbeam antenna radiating arcs of radiation 4along one great circle and one small circle,

FIG. 4 illustrates a pair of shaped beam antennas for use as an inverted V-shaped beam antenna of FIG. 2,

FG. 5 illustrates a section of t-he feed of the slant antenna of FIG. 4,

FIG. 6 illustrates the curvature of the reflector of the slant anntenna of FIG. 4, I

FIG. 7 illustrates a section of the feed of the vertical antenna of FIG. 4,

FIG. 8 illustrates the curvature of the reector of the vertical antenna of FIG. 4, and

FIG. 9 illustrates an arrangement of a three dimensional or 3D radar system in block form utilizing an inverted V-shaped beam antenna.

Referring particularly to FIG. 1, there is shown an illustration of a geometry for an inverted V beam antenna system showing arcs of radiation along two small circles. It should be understood that this invention 1s not limited to two shaped beams, nor is it limited to radiations along small circles; great circle radiations can also be used provided there is at least one shaped beam of a plurality of shaped beams which is oriented along a small circle arc. Particularly, FIG. 1 shows a representation of two shaped beams oriented upon spatial loci, previously unconsidered, which are used to establish one particular spatial coordinate. Typically, this `coordinate can be the elevation angle A as shown in FIG. l. One shaped beam is oriented along the locus of intersection of a unit sphere whose center is at a point and a cone about Y' axis whose cone angle is 2B and whose Vertex is at point 0. This locus is the small circle G', P', S' of the sphere for B=l=90. The Y' axis makes an angle C with the Y axis. For simplicity, the Y axis is shown in the YZ-plane but this is n-ot a restriction on the principle of the invention. The second shaped beam lies along the locus of intersection of the same sphere and a cone about the Y" axis whose cone angle is 2D and whose vertex is also at point 0. This locus is the small circle G", P", S" for D+90". The Y" axis makes an angle E with the Y axis and again, for simplicity only, is pictured in the YZ-plane. According to the values assigned to the angles C, B, E and D, a functional relationship, for example, between the elevation angle A and the angle F measured in a plane parallel to the XY-plane can be solved mathematically for the coordinate A, for each determination of the angle F existing between the corresponding points P', P", one on each shaped beam at the same height lz above the XY -plane. Thus, this arrangement is illustrative of the basic principles involved in considering shaped beams oriented along small circle arcs.

Referring particularly to FIG. 2I there is shown a general arrangement of a beacon helicopter system in block form utilizing an inverted V beam antenna sub-system. There is shown a surface complex 1 having a transmitter 2 of the type generally used in radar systems which could comprise either magnetron or traveling Wave tube power amplifiers or other types of power amplifiers to generate a source of electromagnetic radiation. A power divider 3 is coupled to the transmitter 2 and, in turn, a slant antenna 4 and a vertical :antenna 5, which are adapted for rotation in the surface complex 1 and which comprise the inverted V-beam antenna 6, are coupled to power divider 3. Antenna 4 produces a shaped beam, which will hereafter be called the slant beam which is directed along a small circle arc and the antenna 5, which hereafter will be referred to as the vertical beam antenna, has its radiation directed along a great circle arc. There is also shown a helicopter 7 in a spaced relationship to the surface complex 1. Helicopter 7 includes an antenna 8 for receiving radiations from antennas 4 and 5 of inverted V- beam antenna 6, a receiver 9 coupled to antenna 8 for detecting the radiations of antennas 4 and 5 from inverted V-beam antenna 6, a timer 10 coupled to the receiver 9 for timing the timed difference in the detection of radiations from antennas 4 and 5 from inverted V-beam antenna 6, computer 11 coupled to the timer 10 for calculating the angle of descent of said helicopter 7 to said surface complex 1 and a display 12 for displaying the angle of descent information to the pilot of helicopter 7.

Referring particularly to FIG. 3 and simultaneously considering the operation of the system of FIG. 2, there is shown the geometry of a ground complex surface based beacon helicopter landing system as shown in FIG. 2 having an inverted V-beam antenna sub-system radiating arcs of radiation along one great circle and one small circle. The antennas 4 and 5 of the inverted V-beam antenna 6 are positioned at point 0, point 0 being the center of the sphere of -which one -octant abc is shown in FIG. 3. In the XY and Z rectangular coordinates pictured, the XY-plane represents the surface and the Z axis lpoints to the zenith of the sphere. The shaped beam, approximately 1.5 beamwidth in this case, of the antenna 4, hereafter referred to as the slant beam antenna, is directed along the small circle arc GPV constructed about the Y axis and passing through the zenith point V. This small circle arc is seen to be parallel to only one great circle GLV' on the sphere. The shaped beam, approximately l.5 beamwidth in this case, of the antenna 5, hereafter called the vertical beam antenna, is directed along a great circle arc GPV. The significant radiation of the vertical-ly shaped beam from the vertical beam antenna 5 is contained between 4the elevation angles of approximately 6 to 75 along t-he great circle arc GPV.

The two shaped beams from :antennas 4 and 5 are oriented such that the Ibeam from the vertical beam antenna along the arc GPV is functioning in a conventional Search radar fashion and that of the slant beam along a small circle arc GP'V in a previously unconventional manner. Next, it is shown that by rotating the inverted V-beam antenna 6 about point (l in the surface plane at a constant rate about the Z axis, it is possible that use be made of the angle F, hereafter called the azimuth-response angle, between two points P and P', one on each shaped beam in order to determine the angle of descent that an airborne vehicle, such as helicopter 7 of FIG. 2, hovering on an arc between the point-s P and P', represented by point K, must maintain to arrive at a predetermined point over the surface complex 1.

As the surface based inverted V-beam antenna rotates, consider the effect as seen by a non-directive or omni receiving antenna, such as antenna 8 of helicopter 7 and a detector receiver 9 installed in an airborne helicopter, such as airborne helicopter 7 of FIG. 2, which is hovering at a given altitude which is represented by point K on an arc or a line connecting points P and P' on the shaped beams from antennas 4 and 5 of FIG. 2. Both beams radiated by the inverted V beam antenna 6 will be received and detected sequentially by the helicopter 7. The azimuth-response angle F can be determined by measuring the time between successive detections of the radiation beams from antennas 4 and 5 by the combination of the timer 10 and the receiver 9 of helicopter 7, dividing this time by the time for one rotation of the inverted V-beam beacon antenna sub-system 6 and multiplying the resulting fraction by 360. It is therefore seen that the period -between detection increases in duration as the helicopter moves toward a lower elevation due to increase in spread between the beams at lower elevations. The elevation angle A of FIG. 3 can be determined by the computer 11 of hel-icopter 7 using the timing information from timer 10 to solve the equation sin R Sin F COS A -l-tan C tan A Referring particularly to FIG. 4, there is shown a pair of shaped beam antennas utilized as an inverted V-shaped beam antenna. Although these antennas 4 and 5 are physically separated by such displacement is so minute that for all practical purposes it is considered that they are both located at the same point in space. There is shown a surface complex 1 having a transmitter 2, a power divider 3 coupled to the transmitter 2 and an inverted V-shaped beam antenna 6 coupled to power divider 3. Inverted V-shaped beam antenna 6 comprises a motor `20 for rotating shaft 21. There is shown mounted on shaft 21 a slant antenna 4 tilted at a 20 angle with the horizontal surface 1. Slant beam antenna 4 comprises a reector 22 and a slotted aperture feed 23 positioned at the focal point of reiiector 22. Additionally, mounted on shaft Z1 is shown vertical antenna 5 positioned parallel to surface 1 and rotated 10 with respect to slant antenna 4 about shaft 21. Vertical antenna 5 cornprises a reflector 24 and a slotted aperture feed 25 positioned at the focal point of reflector 24. Additionally, there is shown, mounted on motor 20, a dual channel rotary coupler for feeding energy from power divider 3 to each of the antenna feed-s 23 and 25. The phasing of the antenna feeds causes the antenna beam to radiate along la lar-ge or small circle.

Referring particularly to FIG. 5 and simultaneously to FIGS. 2 and 4, there is shown a section 30y of a feed 23` of slant antenna 4 to illustrate the slotted aperture dimensions of the feed directed toward the reflector 22. For example, in the present embodiment at an operating frequency of 9375 megacycles, section of feed 23y comprises -a piece of RG-SZU waveguide having interior dimensionsv .900" by .400". The waveguide feed 23 comprises an aperture `67 in length having a plurality of slots 31, numbering 110 overall, each .595" long and .125" wide, and being spaced .607" from each other. The spacing and the number of slots has been determined in order to provide a half power beamwidth of 1.5 in the azirnuth-response plane. The slot spacing is determined from Taylors beamwidth aperture length relationship for a -db sidelobe level, see T. T. Taylor, Design of Line Sources for Narrow Beamwidth and Low Sidelobes, Tech. Memo No. 316, Hughes Aircraft Company, July 31, 1953, ASTIA Document Contract No. AF19(604)-262F8, July 31, 1953 and Design of Line- Source Antennas f or Narrow Beamwidths and Low Sidelobes, IRE Transaction on Antennas and Propagation AP-3(1), pp. 16-28, January, 1955, and the standard beam direction formula A a-g '2s where a representsA the phase front inclination to the normal of the waveguide, and where \g=guide wave-length and s=the inter-element spacing, see H. lasik, Antenna Engineering Handbook, McGraw-Hill, New York, pp. 9-11, 9-14, particularly Equations 9-20 on page 9-13, 1961. It is to be understood that the. spacings can be determined for other frequencies and other half power beamwidths -by the above method and using the references as cited. above. Each of the slots 31 are spaced from the centerline 32 of the waveguide 30 as shown in the accompanying Table A, beginning with slot #l and ending with slot #110.

The displacement of the slots from the centerline is determined in accordance with the amount of energy to be extracted from the waveguide feed. The displacements are found sucessively, starting w-ith the slot farthest from the input and using Iasik, Antenna Engineering Handbook, McGraw-Hill, 1961, sections 9-11 through 9-14 for 9375 megacycles. It is to be understood that other spacings would be obtained at different operating frequencies and the said spacing at other operating frequencies could be obtianed by one skilled in the art using the above references.

6 TABLE A.- ELEMENT SLOT DISPLACEMENT FROM CENTERLINE Centerline Centerline Center-line Slot; No. Displacement Slot No. Displace- Slot No. Displace- (Inches) meut ment (Inches) (Inches) l 0.005 Left 0.064 L .005 Right .O65 R .006 L .066 L .005 R .066 R .006 L .067 L .007 R .008 R .007 L .068 'L .007 R .068 R .008 L .069 L .008 R .069 R .008 L .069 L .009 R .069 R .009 L .069 L .010 R .068 R .011 L .068 L .011 R .067.R .012 L .066 L .013 R .065 R .014 L .064 L .014 R .062 R .015 L .060 L .016 R .O58 R .016 L .05er .017 R .054 R .01s L .052 L .019 R .049 R .020 L .047 L .021 R .045 R .022 L .044 L .022 R .042'R .023 L .040 L .024 R .039 R .025 L .038 L` .026 R .038 R .027 L .038 L .028 R 110 0.038 R 0.029 L Load Referring particularly to FIG. 6 and simultaneously to FIGS. 2 and 4, there is shown the curvature of reflector 22 of slant antenna 4. For example, at 9375 megacycles, the focus of reiiector 22 is at a point 15.0 along the positive X axis of FIG. 6. The curvature ofr the reflector is represented by the accompanying Table B, showing X and Y coordinates of the curvature. Particularly point 1 along the curvature is seen from the Table B to be +4624 along the X axis and 7.538 along the Y axis. The other points 2-38 are similarly obtained from the accompanying Table B. The design of the curvature of the slant beam reector is based on geometrical optics considerations. The standard technique appears in the literature, S. Silver, Microwave Antenna Theory and Design, McGraw-Hill, New York, pp. 497-500, 1949; A. S. Dunbar, Calculations of Doubly Curved Reflectors for Shaped Beams, Proc. IRE, vol. 36, pp. 1289-1296, October 1948; H. Jasik, Antenna Engineering Handbook, McGraw-Hill, New York, pp. 12-19 to 12-21, 1961. Referring particularly to Jasik, section 12-20 and solving the equation where and 0 are the primary-and secondary-pattern angle and the subscript values corresponding to the reflector limits and where the energy corersponding between primary I() and secondary power beam pattern 1)(0) is expressed by the above formula, the coordinates as shown in Table B are obtained. It is to be understood that for other operating frequencies the coordinates of the reliector will vary in accordance with known solutions of the above formula.

8 TABLE C.-63 ELEMENT SLOT DISPLACEMENT FROM CENTERLINE TABLE B.-SLANT REF LECTOR l Point X (Inches) Y (Inches) g Point X (Inches) Y (Inches) Referring particularly to FIG. 7 and simultaneously to FIGS. 2 and 4, there is shown a section of feed 25 of vertical antenna 5 to illustrate the slotted aperture dimensions of the feed directed toward the reector 24. For example, at 9375 megacycles there is shown a section 40 of feed comprising a piece of RG-52U waveguide having interior dimensions .900 x .400. The waveguide feed 25 comprises an aperture 60 in length having a plurality of slots 41, numbering 63 overall, each .630 long and .125 wide, and being spaced .950 from each other. The spacing and the number of slots has also been determined for the vertical antenna in order to provide a half power beamwidth of l.5 in the azimuth-response plane. The slot spacing is also determined from Taylors beamwidth aperture length relationship for a -db sidelobe level, sec T. T. Taylor, Design of Line Sources for Narrow Beamwidth and Low Sidelobes, Tech. Memo No. 316, Hughes Aircraft Company, July 31, 1953, ASTIA Document Contract No. AF19(604)262F8, July 31, 1953 and Design of Line-Source Antennas for Narrow Beamwidths and Low Sidelobes, IRE Transaction on Antennas and Propagation AP-3(1) pp. 16-28, January 1955, and the standard beam direction formula where a represents the phase front inclination to the normal of the waveguide, and where Ag: guidewave length and s= the inter-element spacing, see H. Jasik, Antenna Engineering Handbook, McGraw-Hill, New York, pp. 9-11, 9-l4, particularly Equations 9-20 on pages 9-13, 1961. It is to be understood that the spacings can be determined for other frequencies and other half power beamwidths by the above method and using the references as cited above. Each of the slots 41 are spaced from the centerline 42 of the feed waveguide 40, as shown in the accompanying Table C, beginning with Slot #1 and ending with Slot #63. The displacement of the slots from the centerline is determined considering the amount of energy to be extracted from the waveguide feed. The displacements are found successively, starting with the slot farthest from the input and using `lasik, Antenna Engineering Handbook, McGraw-Hill, 1961, sections 9-11 through 9-14 for 9375 megacycles. It is to be understood that other spacings would be obtained at different operating frequencies and the said spacing at other operating frequencies could be obtained by one skilled in the art using the above references.

Ceuterline Ccnterline Centex-line Slot N o. Displacement Slot N o. Displace- Slot N o. Displace- (Inches) meut ment (Inches) (Inches) 1 0.007 Left 039 R .085 L .007 Right .041 L .087 R L 044 R .088 L R 046 L .089 R L 048 R .090 L R 050 L .090 R L .053 R .089 L R 055 L .088 R L 057 R .086 L R 060 L 083 R. L 0.062 R .079 L R 0.064 L .075 R L O67 R .070 L R .069 L .064 R L .071 R .059 L R .074 L .054 R L 076 R 049 L R .078 L .046 R L 080 R .043 L R 082 L .042 R 037 L 084 R 0.042 L Load Referring particularly to FIG. 8 and simultaneously to FIGS. 2 and 4, there is shown the curvature of reector 24 of vertical antenna 5. For example, at 9375 megacycles, the focus of reflector 22 is at a point 15.0 along the positive X axis of FIG. 8. The curvature of the reector is represented by the accompanying Table D, showing X and Y coordinates of the curvature. Particularly, point 1 along the curvature is seen from Table D to be +4624" along the X axis and 7.538 along the Y axis. The other points 2-40 are similarly obtained from the accompanying Table D. The design of the curvature of the slant beam reector is based on geometrical optics considerations. The standard technique appears in the literature, S. Silver, Microwave Antenna Theory and Design, McGraw-Hill, New York, pp. 497-500, 1949; A. S. Dunbar, Calculations of Doubly Curved Reflectors for Shaped Beams, Proc. IRE, vol. 36, pp. 1289-1296, October 1948, and H. Jasik, Antenna Engineering Handbook, McGraw-Hill, New York, pp. 12-19 to 12-21, 1961. Referring particularly to lasik, section 12-20 and solving the equation where qs and 0 are primaryand secondarypattern angles and the subscript values correspond to the reflector limits and where the energy corresponds between primary I() and secondary power beam pattern 13(0) is expressed by the above formula, the coordinates as shown in Table D are obtained. It is to be understood that for other operating frequencies the coordinates of the reflector will vary in accordance with known solutions of the above formula.

TABLE D.--VERTICAL REFLECTOR Point X (Inches) Y (Inches) Point X (Inches) Y (Inches) It is to ybe understood that the speciiic embodiment described for producing shaped beams, is not the only means available for producing shaped beams. For example, other means for producing shaped beams having its significant radiation between 6 and 75 and being conically shaped are taught by Sletten et al. Corrective Line Sources for Paraboloid, IRE Transaction on Antennas and Propagation, vol. AP-6, pp. 248-250, July 1958. Additionally, it is possible to produce shaped beams as shown in lasik, Antenna Engineering Handboo particularly chapter 9, etc., and Silver, Microwave Antenna Theory and Design, particularly chapters 12 and 13. It is, therefore, desired that this invention not be limited to any particular type means for producing shaped beams but rather be solely limited to the structure as claimed in the appended claims.

Referring particularly to FIG. 9, there is shown a 3D radar system in block form utilizing an inverted V-shaped beam antenna. There is shown a surface complex 50 having a transmitter 51 and a receiver 52 coupled to a duplexer 53 which, in turn, is coupled to slant antenna 54 of inverted V-shaped beam antenna 55. The combination being adapted to transmit a shaped beam along a small circle locus from slant antenna 54 and receive reflections from a target, such as aircraft 56, flying above the surface complex. Additionally, there is shown a second transmitter 57 and a receiver 58 coupled to a duplexer 59 which, in turn, is coupled to vertical antenna 60 of inverted V-shaped beam antenna 55. The combination being ad-apted to transmit a vertical shaped beam along a great circle from vertical antenna 60 and receive radiation reflections from `a target, such as an aircraft 56. Additionally, there is shown a computer-display 61 adapted to provide range and azimuth information from reflections received from the vertical antenna which is scanning in the conventional two dimensional radar fashion. Furthermore, computer-display 61 is programmed to compute target height by first determining the elevation angle of the target from the equation sin R cos A as taught in the explanation of FIGS. 2 and 3. Then the height of the target is computed from the known geometrical relationships given by the equation r tangent A=height which is range times tan Azheight, where A is the elevation angle of the target craft with respect to the surface complex.

Other embodiments of the invention can include electronic beam scanning from a fixed aperture in lieu of mechanica-l rotation of the inverted V-beam ant-enna. Additionally, it is possible toobtain greater accuracies if more than two beams are used so as to provide additional redundant information. For example, three shaped slant beams can be used along with one vertical shaped beam so as t` provide additional useable information.

This completes the description of the illustrative embodiments of the present invention. It Will be noted from the foregoing that the present invention provides an antenna system permitting accurate measurement of steeper elevation angles than heretofore in the stat-e of the art and simultaneously provides greater angular response sensitivity due to beam orientation as illustrated in the preferred embodiments. Accordingly, it is desired that this invention not be limited to the particular details of the embodiments disclosed except as defined by the appended claims.

What is claimed is:

1. An inverted V-beam antenna system adapted to scan a portion of a spherical volume of space to provide accurate elevation measurements over a substantially 90 range of angles `and simultaneously provide the greatest sensitivity of measurement at the low elevation angles comprising means for providing a plurality of shaped beams, and means for directing at least one of said plu- Sin F= -l-tan C tan A l@ rality of shaped beams along `a small circle arc intersecting the zenith of said volume such that the spread between said at least `one beam and at least one other beam decreases with increasing height above said antenna system.

2. An inverted V-'beam antenna system comprising a first shaped beam antenna having a reflector and a feed, said reflector and feed, in combination, providing a first shaped beam oriented along a great circle arc, and a second shaped beam antenna having a reflector and feed, said second reflector and feed, in combination, providing a second shaped beam along a small circle arc such that the .spready between said beams always decreases with increasing height above said antenna system so as to proinverted V-beam.

3. An inverted V-beam antenna system comp-rising a first shaped beam antenna, and a second shaped beam antenna, said rst and second antennas providing shaped beams along small circle arcs such that the spread between said shaped beams always decreases with increasing height above said antenna system so as to produce an inverted V-beam.

4. An inverted V-beam system adapted to scan a portion of a spherical volume of space comprising a first shaped beam antenna, a second shaped beam antenna, and means for simultaneously rotating said first and second antennas, said first antenna providing a vertical beam having its principle radiation directed along a great circle arc intersecting the zenith, said second antenna providing a slant beam having its principle radiation directed along a small circle arc intersecting the zenith of said volume such that the spread between said beams decreases with increasing height above said antenna system.

5. An inverted V-beam antenna system adapted to scan a portion of 4a spherical volume of space comprising means for providing a plurality of shaped beams, and means for electronically scanning at least one of said plurality of beams along a lsmall circle arc intersecting the zenith of said volume such that the spread between said at least one beam and at least one other beam decreases with increasing height above said antenna system.

6. A beacon system comprising a surface complex, said surface complex comprising a transmitter, a power divider coupled to said transmitter, first and second shaped beam antennas, each coupled to said power divider, means for simultaneously rotating said first and second antennas, said lfirst and second 'shaped beam antennas radiating a pair of shaped beams, and including means for directing at least one of said shaped beams along a small circle arc such that the spread between said pair of beams decreases with increasing height above said antennas, and a vehicle means in a spaced relationship to said complex, said vehicle means comprising means for detecting said pair of shaped beams radiated from said first and second antennas.

7. A beacon guidance system adapted to scan a portion of a spherical volume of space for helicopter landing operations comprising a surface `based complex, said complex comprising a transmitter, `a first vertical shaped beam antenna coupled to said transmitter, a second slant shaped beam antenna coupled to said transmitter, said first antenna adapted to radiate a first shaped beam oriented along a great circle arc, intersecting the zenith of said volume, said second antenna adapted to radiate a second shaped beam oriented along a small circle arc intersecting the zenith such that the spread between said beams decreases with increasing height above said antennas, an airborne vehicle .adapted for flight in a spaced relationship to lsaid surface based complex, said vehicle comprising means for detecting said first and second shaped radiated beams.

8. A beacon system adapted to scan .a portion of a spherical volume of space comprising means for providing energy for radiation, means for providing a first shaped beam along a great circle intersecting the zenith of `said volume and being coupled to said means for providing energy for radiation, means for providing a second shaped beam along a small circle intersecting the zenith such that the spaced between said beams decreases with increasing height and being coupled to said means for providing energy for radiation, and vehicle means in a spaced relationship to said means for providing said first and second shaped beams, said vehicle means comprising means for detecting said rst and second beams.

9. A beacon system as claimed in claim 8 including means for scanning said rst and second shaped beams.

10. A system adapted to scan a portion of a spherical volume of space for detecting .a target comprising means for providing energy to be radiated, means for providing a first shaped beam along a great circle intersecting the zenith of said volume and being coupled to said means for providing energy to be radiated, means for providing a second shaped beam along a small circle intersecting the zenith such that the spread between said beams decreases with increasing height and being coupled to said means for providing energy to be radiated, and means for determining range, height and azimuth of said target from said system comprising means yfor detecting rst and second beam target reections.

11. A system adapted to scan a portion of a spherical volume of space for detecting a target comprising means for providing energy to be radiated, means for radiating a plurality of shaped beams coupled to said means for providing energy, and means for orienting at least one of said plurality of shaped beams along a small circle arc intersecting the zenith of said volume such that the spread between said at least one beam and at least one other beam decreases with increasing heights, and means for detecting target retlections from said plurality of radiated beams.

12. A three dimensional radar system adapted to scan a portion of a spherical volume of space for determining range, height and azimuth of a target comprising means for providing energy to be radiated, means for providing .a slant beam along a small circle arc intersecting the zenith and being coupled to said means for providing 40 energy to be radiated, means for providing a vertical beam along a great circle arc intersecting the zenith of said volume such that the spread between said beams decreases with increasing height and being coupled to said means for providing energy to be radiated, and means for receiving shaped beam radiation reections from said target.

13. A radar system adapted to scan a portion of a spherical volume of space comprising means for providing energy to be radiated, means for radiating a plurality of shaped beams, vand means for orienting at least one of said shaped beams along a small circle arc intersecting the zenith of said volume such that the spread between said at least one beam and at least one other beam decreases with increasing height and means for receiving radi-ation reflections from said shaped beams hitting a target.

14. A beacon system adapted to scan a portion of a spherical volume of space `for helicopter landing operations comprising means for providing energy to be radiated, means for radiating a plurality of shaped beams, and means for orienting at least one of said shaped beams along a small circle larc intersecting the zenith of said volume such that the spread between said .at least one beam and at least one other beam decreases with increasing height, and means for detecting said beams positioned at a spaced relationship with respect to said means for radiating a plurality of shaped beams.

References Cited by the Examiner UNITED STATES PATENTS 2,245,660 6/1941 Feldman et al. 343-100.6 2,435,988 2/1948 Varian 343-108 2,704,843 3/1955 Longacre 343-11 2,730,715 1/1956 Guanella et al 343-106 2,956,279 10/ 1960 Bartboloma 343-758 2,977,592 3/1961 Bruck 343-108 3,017,628 1/1962 Landee et al 343-5 3,026,517 3/1962 Nameth et al 343-758 3,028,593 4/1962 Cole et al 343-100 3,072,902 1/1963 Bernstein et al. 342-11 3,078,459 2/1963 Vadus et al 343-11 3,102,265 8/1963 Moreau et al 343-100 CHESTER L. JUSTUS, Primary Examiner.

E. T. S. CHUNG, P. M. HINDERSTEIN,

Assistant Examiners. 

1. AN INVERTED V-BEAM ANTENNA SYSTEM ADAPTED TO SCAN A PORTION OF A SPHERICAL VOLUME OF SPACE OF PROVIDE ACCURATE ELEVATION MEASUREMENTS OVER A SUBSTANTIALLY 90* RANGE OF ANGLES AND SIMULTANEOUSLY PROVIDE THE GREATEST SENSITIVITY OF MEASUREMENT AT THE LOW ELEVATION ANGLES COMPRISING MEANS FOR PROVIDING A PLRALITY OF SHAPED BEAMS, AND MEANS FOR DIRECTING AT LEAST ONE OF SAID PLURALITY OF SHAPED BEAMS ALONG A SMALL CIRCLE ARC INTERSECTING THE ZENITH OF SAID VOLUME SUCH THAT THE SPREAD BETWEEN SAID AT LEAST ONE BEAM AND AT LEAST ONE ANOTHER BEAM DECREASES WITH INCREASING HEIGHT ABOVE SAID ANTENNA SYSTEM. 